Transistor t-r series switch with collector-emitter capacitance tuned with anti-resonant circuit



June 10, 1969 C..PACE TRANSISTOR T-R SERIES SWITCH WITH COLLEC TOR-EHITTER CAPACITANCE TUNED WITH ANTI-RESONANT CIRCUIT Filed Aug. 4. 1964 fizrlz rz CI Pecq BY M MM2= v ATTORNEYS United States Patent 3 449 674 TRANSISTOR T-R SER IES SWITCH WITH COLLEC- TOR-EMITTER CAPACITANCE TUNED WITH ANTI-RESONANT CIRCUIT Nevlin C. Pace, 4306 N. 40th St., Arlington, Va. 22207 Filed Aug. 4, 1964, Ser. No. 387,319 Int. Cl. H04]: 1/44; H04] 5/00 US. Cl. 325-21 1 Claim This invention relates to communication systems and more particularly it relates to the switching of a single antenna for use by either a receiver or a transmitter.

Because of the difference in power requirements between transmission and reception circuits, and the presence of R-F energy, it has long been a problem in switching a single antenna between a receiver and transmitter. The use of relay contacts for transmitter switching is not satisfactory because of the large amount of R-F power involved and the rugged nature of the contacts, which encourages pitting and arcing.

Conversely the energy level upon reception is so small that losses in relay contacts or switch blades are significant, and similar performance cannot be expected every switching cycle. Yet either a remote control or automatic device is desirable for such switching. While the relay can be remotely controlled and certain types of automatic gaseous tube devices with tuned cavities can use transmitter energy to produce switching at very high frequencies, no acceptable switching device has been available in the prior art for such switching at electronic speeds while providing satisfactory performance with both conditions of high transmitter R-F power requirements and low level reception signals.

Accordingly it is the object of this invention to provide an improved antenna switch.

Thus, in accordance with the invention, an antenna is switched from transmitter to receiver by use of a transistorized switching circuit. The transistors have special circuit configurations permitting them to handle R-F energy with little attenuation, and to permit them to become essentially open or closed circuits respectively with close to infinite and zero impedance.

The particular circuit configuration of a typical embodiment is shown in the accompanying drawing.

It may be seen that the antenna 5 is connected through shielded coaxial cable 6 to the emitter electrodes of both a PNP transistor 7 and an NPN transistor 8. These transistors respectively serve as switches for connecting the antenna 5 to either transmitter 10 or receiver 11, dependent upon the polarity of switching potential 12 received at the common base input terminal 14 for both transistors. In this manner antenna changeover can occur responsive to high-speed low-power electronic pulses without employing unreliable relay contacts.

In a simplex transmission channel it may be assumed the transmitter and receiver are on fixed frequencies and thus the various tuned circuits in this embodiment may all be tuned to the same frequency. For example, the parallel tuned circuits 20, 21 between the base electrodes of the transistors 7, 8 and the base input terminal 14 are tuned anti-resonant circuits presenting high impedance to avoid losing R-F through the base. Resistors 22, 23 are the usual D-C base current-limiting resistors for the transistors.

Because of distributed capacity C across the emittercollector paths of the transistors, they cannot alone be used effectively as R-F switches, since when D-C current flow ceases, R-F can flow through the capacitance C. However the anti-resonant tuned circuits 24, 25 including the inherent capacity C effectively blocks the R-F when the current flow is cut off. Shunt capacitor C is used in these tuned circuits 24, 25 to provide a large enough tuned circuit capacitance in shunt with the emitter-collector path to swamp out any minor capacity variations in C which might tend to detune the circuit.

When current flows through the emitter-collector path, essentially the high impedance tuned circuit is shorted out, and the R-F path through the transistor is established. Potential sources at terminals 30, 31 provide the D-C current for operation of the switches. Each source is decoupled by a resistor-capacitor circuit 32, 33 respectively from the R-F in coils 34, 35.

In the case of receiver 11, energy is received from antenna 5 through transistor 8 at input R-F circuit coils 35. Transmitter 10 couples its output power through coils 34 and transistor 7 to antenna 5. By use of the NPN-PNP combination, only one transistor may conduct at any one time and therefore only the transmitter or the receiver is connected to the antenna, so that there is no possibility of damaging receiver 11 for example with full transmitter power not blocked by anti-resonant circuit 25.

Should the coaxial antenna lead 6 not be at DC ground, a further anti-resonant circuit 40 may be coupled into circuit to provide a current return path for the transistors with little loss of R-F power.

It is evident therefore that this invention has in an improved manner provided for electronic antenna switching with semi-conductors. Accordingly those novel features believed descriptive of the nature of the invention are defined with particularity in the appended claims.

What is claimed is:

1. In combination a first transistor with collector, emitter and base electrodes, a receiver having an R-F input stage coupled to said collector electrode to receive current therefrom, an antenna connected to said emitter electrode to pass current thereto, D-C potential means connected to pass transistor current through said emittercollector path, an anti-resonant circuit tuned to the receiver R-F frequency coupled between said emitter and collector, a second transistor having collector, base and emitter electrodes, one of said transistors being NPN and the other PNP, a transmitter R-F output stage connected to said collector of the second transistor to receive R-F current therefrom, said antenna connected also to the emitter electrode of said second transistor to pass R-F current therefrom, and switching means connected to the bases of both transistors to set one in a conduction state upon receipt of a negative potential and to set the other in a conduction state upon receipt of a positive potential, thereby electronically switching the antenna to transmitter or receiver.

(References on following page) 3 4 References Cited 3,131,365 4/1964 Hoover 333-7 UNITED STATES PATENTS 3,139,584 RFrednckson 325-362 E EF N 12/1955 Sziklai 307-254 PHI A ti s iz D b 3/1960 Miller 325-169 X 5 1960} PP a mm er 4/1960 Endres et a1. 325-318 Eberhard X L. Primary Examiner. 5 1957 i i 332 52 B. V. SAFOUREK, Assistant Examiner. 12/1958 Lehman et a1. 307255 10 U.S. Cl. X.R. 12/1962 Lewis 307 255 X 343-180 

1. IN COMBINATION A FIRST TRANSISTOR WITH COLLECTOR, EMITTER AND BASE ELECTRODES, A RECEIVER HAVING AN R-F INPUT STAGE COUPLED TO SAID COLLECTOR ELECTRODE TO RECEIVE CURRENT THEREFROM, AN ANTENNA CONNECTED TO SAID EMITTER ELECTRODE TO PASS CURRENT THERETO, D-C POTENTIAL MEANS CONNECTED TO PASS TRANSISTOR CURRENT THROUGH SAID EMITTERCOLLECTOR PATH, AN ANTI-RESONANT CIRCUIT TUNED TO THE RECEIVER R-F FREQUENCY COUPLED BETWEEN SAID EMITTER AND COLLECTOR, A SECOND TRANSISTOR HAVING COLLECTOR, BASE AND EMITTER ELECTRODES, ONE OF SAID TRANSISTORS BEING NPN AND THE OTHER PNP, A TRANSMITTER R-F OUTPUT STAGE CONNECTED TO SAID COLLECTOR OF THE SECOND TRANSISTOR TO RECEIVE R-F CURRENT THEREFROM, SAID ANTENNA CONNECTED ALSO TO THE EMITTER ELECTRODE OF SAID SECOND TRANSISTOR TO PASS R-F CURRENT THEREFROM, AND SWITCHING MEANS CONNECTED TO THE BASES OF BOTH TRANSISTORS TO SET ONE IN A CONDUCTION STATE UPON RECEIPT OF A NEGATIVE POTENTIAL AND TO SET THE 